1. Field of the Invention
The present invention relates to an optical scanning device and an image forming apparatus.
2. Description of the Related Art
An optical scanning device in a color image forming apparatus has a problem that a curvature and a tilt occur in a laser scanning line in forming an electrostatic latent image on a photosensitive element as an image carrier.
The problem is caused by characteristics of a field curvature of an optical element, a distortion of an optical housing, a thermal deformation due to a heat generation of a polygon motor, a thermal deformation due to a heat generation of units generating heat such as a fixing unit in a main body of an image forming apparatus, and a distortion of a photosensitive element in installation.
The occurrence of the curvature and the tilt in a scanning line causes a color deviation since three or four scanning lines do not overlap in a color image forming apparatus.
To deal with the problem, known is a technique for adjusting, while keeping a state where curvature of a scanning line is adjusted, an amount of tilt, occurring due to a thermal change in an image forming apparatus, of a scanning line as disclosed in Japanese Patent No. 4951242.
As illustrated in FIG. 3 in the adjustment technique disclosed in Japanese Patent No. 4951242, a deflection amount (Z direction) of an elongated lens as an optical element is controlled by a scanning line curvature adjusting unit which is attached to a bracket serving as a retaining member.
A tilt amount can be adjusted by a rotation on an axis of an X direction, by a driving motor of a tilt adjusting unit, of the elongated lens while the adjusted deflection amount is maintained.
From a standpoint of a desired precision in lens attachment, it is necessary to cause the elongated lens to be in direct contact with a positioning unit provided in the optical housing with respected to the X direction (optical axis direction).
For the positioning, both end parts of the elongated lens are pressed to the X direction by a plate spring 102 which is fixed to an optical housing 100 to cause the elongated lens 5 to be in direct contact with a positioning unit 104 formed in the optical housing, as illustrated in FIG. 19.
A direct contacting part 5-3 projecting outward from the both end parts of the elongated lens 5 comes to have a direct contact with the positioning unit 104 by a biasing force (pressure force) of the plate spring 102 and the elongated lens 5 is thus positioned in the optical axis direction.
The both end parts of the elongated lens 5 are retained in a bracket 21 by plate springs 23 and 24.
As explained above, it is necessary to perform a rotating operation on an axis, as a rotation center, of the X direction in adjusting a tilt amount of the elongated lens.
In this case, a pressure force F1 by the plate spring 102 intersects with a rotation force F2 and serves to prevent the rotation force F2.
The pressure force by the plate spring 102 also serves to prevent a displacement in position of the elongated lens due to an impact, a vibration, and the like toward the optical axis direction in the course of distribution and the like.
Therefore, while being required to be sufficiently large, the pressure force by the plate spring 102 becomes a factor of generating a frictional force between the elongated lens and the positioning unit in the optical axis direction of the optical housing and hence disturbs the rotating operation in adjusting the tilt.
To perform the tilt adjusting operation satisfactorily in this contradictory force relationship, a design of a plate spring to be mounted becomes highly delicate and thereby a tolerance needs to be set strictly, which results in the plate spring with higher cost than a normal plate spring.
Besides, there are some cases where all components are not necessarily as good as designed in mass production and the pressurizing system by plate springs does not have a robust structure against disturbance from a stand point of robustness in regard to part variation.
Low robustness means no room for adjustments in range and precision in the structure.
Therefore, there is a need for an optical scanning device capable of securing enough room for adjustment in range in adjustment of curvature of a scanning line, suppressing variation in adjustment precision, and contributing to a reduction in cost as a result of a reduction in the number of components to be mounted.